Traditional foam-in-place structural materials known in the art generally disclose polyurethane, polyurea materials or epoxy-based materials with or without a blowing agent. These materials are typically composed of a mixture of ingredients to enable expansion and curing to occur at rates that enable development of a cured cellular product. For example, commonly assigned U.S. Pat. No. 5,648,401 for Foamed Articles And Methods Of Making Same, which is hereby expressly incorporated by reference, teaches a three-ingredient foam-in-place structural material. Although these prior art materials are both useful and successful in a number of applications for purposes that include acoustics and sealing, certain applications in the automotive, construction, aerospace, and other industries would benefit from a material having a rapid curing foam-in-place material with the ability to be tailored to fit various applications without using toxologically undesirable materials such as isocyanate functional chemicals, or liquid amines.
As known by those skilled in the art, a number of factors determine the suitability of a process for forming a foamed product of the type in which a blowing agent forms cells in a synthetic resin as the resin is cured. Most significantly, the interaction of the rate of cure and the rate at which the blowing gas is generated must be such that the correct foam volume is attained. If the resin cures too rapidly there is inadequate time for the gas to form the proper size and number of gas voids in the finished product. Over expansion of the forming foam product must also be avoided. Rapid expansion due to a slow cure rate may cause the expanding foam to simply collapse as a result of inadequate wall strength surrounding the individual gas cells.
Generally speaking, foamed products must have good stability when exposed to various environmental conditions and, most significantly, in many applications they must protect metal from corrosion when exposed to hostile environmental conditions. This is particularly true in automotive applications where the foamed product can be utilized and placed within portions of the vehicle that are routinely exposed to hostile environmental conditions, ambient temperature and weather fluctuations, as well as structural stress and strain.
In the past, many foamed parts were made using polyurethane which provides a number of desirable attributes. It is known, however, that alternatives to urethane-based or urea-based foams are frequently more environmentally desirable. Such environmental concerns relate to material handling during manufacturing as well as waste management concerns, in part due to unreacted functional groups in the finished products and difficulty in handling isocyanate functional chemicals in manufacturing processes.
Accordingly, there is a need in industry and manufacturing operations for a foam-in-place material, particularly one that may be structural with corresponding mechanical properties but without the negative attributes based on foams created using isocyanate chemistry. The present invention addresses and overcomes the shortcomings found in the prior art by providing a first epoxy component formulated with a thermoplastic shell that encapsulates a physical blowing agent. A second component consisting of an acid, and preferably a strong acid is then combined with the first epoxy component to produce a reactive mixture foam-in-place material which when cured demonstrates good adhesion to metallic substrates and good resistance to high humidity or corrosive environments when compared to foam-in-place materials known in the art.